Post-transcriptional gene silencing (PTGS)-mediated gene silencing exploits the cellular mechanism wherein transcripts having sequence similarity to the double-stranded RNA (dsRNA) molecules present in the cell will be subjected to degradation. PTGS is closely related to natural processes such as RNA-mediated virus resistance and cross-protection in plants. Gene silencing and the cellular machinery for affecting this phenomenon might have evolved as a natural protective measure against viral infection in plants. In PTGS, small interfering RNA (siRNA) molecules of 21–23 nucleotides length act as homology guides for triggering the systemic degradation of transcripts homologous to the siRNA molecules. PTGS phenomenon, first discovered in transgenic petunia plants harbouring chalcone synthase gene and termed co-suppression, has been subsequently exploited to target specific gene transcripts for degradation leading to manifestation of desirable traits in crop plants. Targeted gene silencing has been achieved either through the introduction of DNA constructs encoding dsRNA or antisense RNA or by deploying co-suppression constructs producing siRNAs against the transcript of interest. Understanding the mechanism of gene silencing has led to the development of several alternative strategies for inducing gene silencing in a precise and controlled way. This has paved the way for using PTGS as one of the chief functional genomics tools in plants and has helped in unraveling the mechanism of many cellular processes and identifying the focal points in pathways, besides, opening new vistas in genetic engineering of plants for human benefits. PTGS has shown great potential in silencing the deleterious genes efficiently so that value-added plant products could be obtained. Thus, PTGS has ushered in a new era in the genetic manipulation of plants for both applied and basic studies. In this review, we have outlined the basics of RNAi-mediated gene silencing and summarized the work carried out at our institute using this approach, as case studies. In particular, adopting RNAi-mediated gene silencing (a) as a method to restore fertility in transgenic male sterile lines developed based on orfH522 gene from sunflower PET1-CMS source, (b) as a tool to suppress the production of toxic proteins, ricin and RCA, in castor, and (c) as an approach to induce bud necrosis virus resistance in sunflower has been discussed. Examples from other plant systems also have been mentioned to exemplify the concept and utility of gene silencing in crop plants.

中文翻译：

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转录后基因沉默：基本概念和应用

转录后基因沉默 (PTGS) 介导的基因沉默利用细胞机制，其中与细胞中存在的双链 RNA (dsRNA) 分子具有序列相似性的转录物将受到降解。PTGS与植物中RNA介导的病毒抗性和交叉保护等自然过程密切相关。基因沉默和影响这种现象的细胞机制可能已经演变为一种针对植物病毒感染的天然保护措施。在 PTGS 中，长度为 21-23 个核苷酸的小干扰 RNA (siRNA) 分子作为同源向导，触发与 siRNA 分子同源的转录本的系统降解。PTGS 现象，首先在含有查尔酮合酶基因的转基因矮牵牛植物中发现，称为共抑制，随后被用于靶向特定基因转录本进行降解，从而导致作物植物中所需性状的表现。靶向基因沉默已经通过引入编码 dsRNA 或反义 RNA 的 DNA 构建体或通过部署产生​​针对目标转录物的 siRNA 的共抑制构建体来实现。对基因沉默机制的理解导致开发了几种以精确和受控方式诱导基因沉默的替代策略。这为使用 PTGS 作为植物中的主要功能基因组学工具之一铺平了道路，并有助于解开许多细胞过程的机制并确定途径中的焦点，此外，为人类造福植物基因工程开辟了新的前景. PTGS 在有效沉默有害基因从而获得增值植物产品方面显示出巨大潜力。因此，PTGS 为应用和基础研究开创了植物遗传操作的新时代。在这篇综述中，我们概述了 RNAi 介导的基因沉默的基础知识，并总结了我们研究所使用这种方法进行的工作，作为案例研究。特别是，采用 RNAi 介导的基因沉默 (a) 作为恢复基于向日葵 PET1-CMS 来源的 orfH522 基因开发的转基因雄性不育系的生育力的方法，(b) 作为抑制有毒蛋白质、蓖麻毒素产生的工具已经讨论了蓖麻中的 RCA 和 (c) 作为在向日葵中诱导芽坏死病毒抗性的方法。